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<h1>Table of Contents</h1>

<ul>
	<li><a href="#objective">Objective</a></li>
	<li><a href="#variations">Game Variations</a></li>
	<ul>
		<li><a href="#grids">Grid Styles</a></li>
		<li><a href="#extras">Extra Regions</a></li>
	</ul>
	<li><a href="#difficulties">Levels of Difficulty</a></li>
	<li><a href="#inputmethods">Input Methods</a></li>
	<ul>
		<li><a href="#im_ctv">Cell Then Values</a></li>
		<li><a href="#im_vtc">Values Then Cell</a></li>
		<li><a href="#im_auto">Automatic</a></li>
	</ul>
	<li><a href="#links">External Links</a></li>
</ul>

<h1 id="objective">Objective</h1>

<p>The objective of the game is to fill the entire game grid so that
the digits from 1 to 9 appear exactly once in each <i>region</i>. For a
standard sudoku a <i>region</i> is either a row, a column or one of the
nine square 3x3 blocks.</p>

<h1 id="variations">Game Variations</h1>

<p>Andoku offers additional sudoku variations besides the classical
one. In the <i>New Game</i> menu you can choose from two grid styles and
five kinds of extra regions.</p>

<h2 id="grids">Grid Styles</h2>

<p>The available grid styles are:</p>
<dl>
	<dt>Standard</dt>
	<dd>The grid is made up of square 3x3 blocks.</dd>
	<dt>Squiggly (a.k.a. jigsaw)</dt>
	<dd>Instead of 9 square blocks the game grid consists of 9
	non-square regions. The regions are outlined with a thick line and the
	digits 1 to 9 have to appear exactly once in each region.</dd>
</dl>

<h2 id="extras">Extra Regions</h2>

<p>Extra regions impose additional constraints on the puzzle.
Besides the classic version there are four kinds of extra regions:</p>
<dl>
	<dt>None</dt>
	<dd>You only have to deal with nine rows, nine columns and nine
	blocks in either square or squiggly format.</dd>
	<dt>X-Sudoku</dt>
	<dd>The digits 1 to 9 also have to appear exactly once in the two
	diagonals of the puzzle. To indicate this the diagonals of the puzzle
	are highlighted by a different color.</dd>
	<dt>Hyper-Sudoku</dt>
	<dd>This sudoku has four additional regions highlighted in a
	different background color. In addition to rows, columns and blocks the
	digits 1 to 9 have to appear exactly once in each of these extra
	regions.</dd>
	<dt>Percent-Sudoku</dt>
	<dd>The sudoku has three additional regions that resemble a
	percent sign.</dd>
	<dt>Color-Sudoku</dt>
	<dd>This sudoku has nine additional regions. Each one of these
	regions is highlighted by a distinct color so there are nine different
	background colors. The digits 1 to 9 have to appear exactly once in all
	cells that have the same background color.</dd>
</dl>

<h1 id="difficulties">Levels of Difficulty</h1>

<p>Andoku offers five levels of difficulty per game type. The
difficulties range from <i>Easy</i> to <i>Fiendish</i>. Squiggly sudokus
or sudokus with extra regions are generally more difficult than standard
sudokus.</p>

<p>The levels of difficulty <i>Hard</i> and <i>Fiendish</i> should
contain harder puzzles than what can be found in newspapers.</p>

<p>With ten different game types, five levels of difficulty and 100
puzzles per type and difficulty Andoku offers a total of 5000 puzzles.</p>

<h1 id="inputmethods">Input Methods</h1>

<p>Andoku offers three different input methods for entering digits
into the cells of a puzzle while playing. Go to Settings to choose
between the available input methods.</p>

<h2 id="im_ctv">Cell Then Values</h2>

<p>With this input method you first select a cell by tapping on it
with your finger and then you use the numeric pad at the bottom of the
screen to enter one or more possible values for that cell. The selected
cell will be highlighted with a background color.</p>

<p>Press the button <tt>C</tt> to clear the values of the selected
cell.</p>

<p>The button <tt>Inv</tt> (Invert) is used to reverse the values of
the current cell. This makes it possible to easily specify that certain
values are <i>not</i> possible in a certain cell. For example if you
enter <tt>3</tt>, <tt>7</tt>, <tt>Inv</tt> the result will be 1, 2, 4,
5, 6, 8 and 9 (all digits except 3 and 7).</p>

<p>If the device has a trackball it can be used to move the
selection to one of the neighbor fields.</p>

<h2 id="im_vtc">Values Then Cell</h2>

<p>This input method works in reverse. First select one or more
values from the numeric pad at the bottom of the screen. Only then can
you tap on a cell to assign these values.</p>

<p>This input method can save a lot of time because it is possible
to assign the same value or values to multiple cells by tapping on
different cells one after the other.</p>

<p>But what happens when you tap on a cell that is not empty? The
result depends on whether the cell already contains one of the selected
values or not. If the cell does not already contain one of the selected
values the values are simply added (same behavior as if the cell is
empty). If, on the other hand, the cell already contains one of the
selected values then all of the selected values will be reset.</p>

<p>Example 1: if cell value is <tt>3</tt>, numeric pad contains <tt>5</tt>
and <tt>7</tt>, this results in 3, 5 and 7.</p>

<p>Example 2: if cell values are <tt>3</tt>, <tt>5</tt> and <tt>7</tt>,
numeric pad contains <tt>3</tt> and <tt>5</tt>, this results in 7.</p>

<p>Example 3: if cell values are <tt>3</tt> and <tt>5</tt>, numeric
pad contains <tt>5</tt> and <tt>8</tt>, this results in 3. I.e. 5 is
cleared, but 8 is <i>not</i> set.</p>

<p>The button <tt>C</tt> is used to clear all values on the numeric
pad. The button <tt>Inv</tt> is used to reverse the values on the
numeric pad.</p>

<p>Example 4: if cell values are <tt>3</tt>, <tt>5</tt> and <tt>7</tt>,
suppose you think the correct value ought to be 5. An easy way to remove
all values except 5 is to press <tt>5</tt> followed by <tt>Inv</tt> and
then to tap on the cell.</p>

<h2 id="im_auto">Automatic</h2>

<p>Use this input method if you want to easily switch back and forth
between <i>Cell Then Values</i> and <i>Values Then Cell</i>.</p>

<p>This means that initially both input methods are possible. If you
tap on a cell first then <i>Cell Then Values</i> will be used
automatically. If you tap on a digit of the numeric pad first then <i>Values
Then Cell</i> will be used instead.</p>

<p>If you want to get back to the neutral state from <i>Cell
Then Values</i> you have to tap on the selected cell a second time.</p>

<p>To get back from <i>Values Then Cell</i> you have to clear all
values on the numeric pad. The simplest way to do this is by pressing
the button <tt>C</tt>.</p>

<h1 id="links">External Links</h1>

<p>Andoku is an open source project. The project's home page is
hosted at <a href="http://code.google.com/p/andoku">Google Code</a>.</p>

<p>For more information on Sudoku puzzles in general see <a
	href="http://en.m.wikipedia.org/wiki/Sudoku">Wikipedia: Sudoku</a>.</p>

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